The study finds significant differences between the three assessments and also finds that the independent assessments of forcing and climate sensitivity within AR5 are not consistent if one assumes the simple energy balance model to be a perfect description of reality.[Doubtful that Bengtsson's paper would claim any model was a "perfect description of reality"]

The overall innovation of the manuscript is very low, as the calculations made to compare the three studies are already available within each of the sources, most directly in Otto et al. [What's wrong with a paper that reviews compiles data/models from different studies to show consistencies & inconsistencies? There are tens of thousands of such published papers in the scientific literature]

The finding of differences between the three "assessments" and within the assessments (AR5), when assuming the energy balance model to be right, and compared to the CMIP5 models are reported as apparent inconsistencies.[Again doubtful that Bengtsson made the claim that any model was "right" or a "perfect description of reality"]

The paper does not make any significant attempt at explaining or understanding the differences, it rather puts out a very simplistic negative message giving at least the implicit impression of "errors" being made within and between these assessments, e.g. by emphasising the overlap of authors on two of the three studies. [In other words, Bengtsson's paper did not actually accuse any other authors of errors, and this "implicit impression" is the opinion of the reviewer]

What a paper with this message should have done instead is recognising and explaining a series of "reasons" and "causes" for the differences. [why the quote marks around "reasons" and "causes"? These would be mere speculation anyway given the black box nature of climate models]

- The comparison between observation based estimates of ECS and TCR (which would have been far more interesting and less impacted by the large uncertainty about the heat content change relative to the 19th century) and model based estimates is comparing apples and pears, as the models are calculating true global means, whereas the observations have limited coverage. This difference has been emphasised in a recent contribution by Kevin Cowtan, 2013. [Cowtan debunked]

- The differences in the forcing estimates used e.g. between Otto et al 2013 and AR5 are not some "unexplainable change of mind of the same group of authors" but are following different tow different logics, and also two different (if only slightly) methods of compiling aggregate uncertainties relative to the reference period, i.e. the Otto et al forcing is deliberately "adjusted" to represent more closely recent observations, whereas AR5 has not put so much weight on these satellite observations, due to still persisting potential problems with this new technology. [Paraphrasing, satellite observations are newfangled technology that can’t be trusted, but climate models are golden. And as if the tampered, up-justed, UHI contaminated surface thermometer record is superior to satellite observations]

- The IPCC process itself explains potential inconsistencies under the strict requirement of a simplistic energy balance: The different estimates for temperature, heat uptake, forcing, and ECS and TCR are made within different working groups, at slightly different points in time, and with potentially different emphasis on different data sources. The IPCC estimates of different quantities are not based on single data sources, nor on a fixed set of models, but by construction are expert based assessments based on a multitude of sources. Hence the expectation that all expert estimates are completely consistent within a simple energy balance model is unfunded from the beginning.

- Even more so, as the very application of the Kappa model (the simple energy balance model employed in this work, in Otto et al, and Gregory 2004) comes with a note of caution, as it is well known (and stated in all these studies) to underestimate ECS, compared to a model with more time-scales and potential non-linearities (hence again no wonder that CMIP5 doesn't fit the same ranges). [Otto et al finds equilibrium climate sensitivity [ECS] at the top of the atmosphere is only slightly higher [1.3X] than transient climate sensitivity [TCS]]

Summarising, the simplistic comparison of ranges from AR4, AR5, and Otto et al, combined with the statement they they are inconsistent is less then helpful, actually it is harmful as it opens the door for oversimplified claims of "errors" and worse from the climate sceptics media side. [i.e. this rejection is all about politics, not science, and this confirms the clear bias of the reviewer]

One cannot and should not simply interpret the IPCCs ranges for AR4 or 5 as confidence intervals or pdfs and hence they are not directly comparable to observation based intervals (as e.g. in Otto et al).

In the same way that one cannot expect a nice fit between observational studies and the CMIP5 models.[Thus, expecting the models to agree with observed reality is considered to the error of Bengtsson's paper]

A careful, constructive, and comprehensive analysis of what these ranges mean, and how they come to be different, and what underlying problems these comparisons bring would indeed be a valuable contribution to the debate.

I have rated the potential impact in the field as high, but I have to emphasise that this would be a strongly negative impact, as it does not clarify anything but puts up the (false) claim of some big inconsistency, where no consistency was to be expected in the first place.[false, of course there should be at least some consistency between models and observations]

And I can't see an honest attempt of constructive explanation in the manuscript.

Thus I would strongly advise rejecting the manuscript in its current form.

2 comments:

"the models are calculating true global means, whereas the observations have limited coverage"

This is like saying that the average of all the guesses of the length of the emperor's nose (made by people who have never seen the emperor's nose) calculates the true length of his nose, but the observations that some have made by telescope are not reliable, because they measure too small a portion of his nose (have limited coverage).

Wow. If disagreement with measured values does not necessitate revision of a model, or falsify it outright, we're in trouble!

Yes exactly, that is the premise of climate pseudo-science, that if the observations don't agree with the models, there must be something wrong with the observations. Lindzen, Spencer, Christy, Singer and many others have been pointing out this obvious inversion of the scientific method for many years.